Opponents of the 1080 poison have forced DoC to admit it uses the private investigators to monitor their social media, costing $103,187.

However, DoC has since denied ordering them to spy.

"The Department of Conservation has not contracted Thompson and Clark Limited or any other investigator to undertake surveillance," it told Newshub.

Opponent of 1080 Clyde Graf says he's "not surprised, but it is concerning". Those who want use of the controversial poison stopped say they have caught people photographing them on protests.

Newshub asked both police and Thompson & Clark if the photographers worked for them - both denied it.

DoC would not appear on camera, but said anti-1080 activists subject its staff to intimidation and threats - including threats to kill.

DoC admitted using Thompson and Clark for:

Government Protective Security Requirements (PSR)

Security awareness training

Security assessments

Monitoring threats

And it seems a 'matey' relationship between Thompson and Clark and the New Zealand Security Intelligence Service (SIS) spy agency may have helped get them the contract for the PSR work - protecting government departments against threats.